[@CaptainSully]

After a quick read through, there's a few things I'd like changed.
You might need to adjust his stats, and I'll explain why.

I feel like my explanation of stats is a bit lackluster, so I'll throw a thing down here.

Consider the base stat, D, for Physical Competence.
D is the base human stat, the average of human ability.
However, due to the nebulous nature of the stats, I've recently decided on a scale that allows both normal humans to be compared to things like Deities and Demons.
How it works is, with D being your average human ability, C would be twice the capability. B would then be double that (quadruple), A would double that again, S would double the A score, etc.
EX is limited to things that 'cannot be measured'.

The scale goes as such:
E (Lower than average human)
D (Average human)
C (Double average human)
B (Double C)
A (Double B)
S (Double A)
S+ (Double S)
SS (Double S+)
SSS (Double SS)
X (Double SSS)
EX (Anything above X)

Admittedly that's my fault but originally I made the stat system with only myself in mind, so not properly explaining is my problem. Sorry!
With that in mind, I should also talk about 'Faith'.

It's not so much Faith in religious terms as much as it's 'Faith in outcomes'. The Faith stat is 'I have Faith this will happen'. So when a Mage uses a Spell they use Willpower to 'force' the change on Reality and Faith to 'believe the change will occur', hence why a high Willpower and Faith are required to use something as insane as a Boundary (which are always pretty crazy).

In relation, could you add clauses to his Passive True Mind that allow those with higher Willpower than himself to negate this Passive? The Willpower stat is actually really, really important, so I made a pretty big mistake by not properly explaining it.

Willpower is.. a very difficult stat to be honest. A person with zero Magickal prowess might actually have a Willpower of A or even S. Willpower can also be described as 'determination'. Like the term 'iron will'. Having a higher Willpower stat means you're capable of resisting the Magick of other people with lower of equal Willpower. It follows the same rules as Physical Competence, but know that having an EX Willpower is meant for beings who're Divinity and the like.
For a regular human with no formal training or boosts (as Willow could easily be giving him) the highest Willpower stat would be C. With training, a person can reach higher ranks, but without training they'd be around the average or slightly above.

Aside from that, he looks great, although I'll reread just in case there's anything I forgot.
I know the majority of my criticism is due to my lack of explanation so that's my fault.

However, I really like what you've got going for him so far. We may have to have a chat about Willow in the future (because I'm interested in what Willow is) and I also really like how you handled his time ability. Whenever I see time travel I tend to cringe, but you hit a really good spot as he can't derail the timeline and it doesn't give him a 'full reset' to get out of horrible situations.
Can he interact with his past self, though?

Also, I really enjoy the concept of a not super-strong guy kinda tricking people into thinking he's super strong because he's super fast and nobody could really tell the difference.

This went on a bit longer than I'd meant it to, but Leolin's looking good so far!

Edit: Jesus Christ this was long mfw